Patent Application
20120033780
The present invention relates to a technique of controlling an axial power distribution of a nuclear reactor, and more particularly relates to a technique of preventing a xenon oscillation that can be generated in a pressurized water reactor.
It is widely known that a xenon oscillation could occur in the pressurized water reactor (PWR). The xenon oscillation is observed in the form of spatial oscillation of power distributions due to variations in spatial xenon concentration distribution. Xenon is a fission product from nuclear fission and has a high neutron absorption capability.
Xenon oscillation involves significant power distribution distortion in a nuclear reactor and may cause excessive local power, resulting in the local temperature rises. In order to ensure the safety of the core, xenon oscillation must be suppressed within a range of safe plant operation.
One of the technologies for preventing the above-mentioned excessive distortion of power distribution is known as “Power Distribution Control Method” for keeping axial power distribution within a prescribed range. For example, the Constant Axial Offset Control Method controls an axial offset (AO) within an allowable range which is determined based on the target-AO. Where, the AO is defined as a fraction of the power difference in the upper and lower halves of the core, and the target-AO is defined as the AO at which the core power is stable with control rods being almost totally withdrawn. In operation, it is monitored whether AO (or a value calculated by multiplying AO by the relative power when the core is at partial power) is within the allowable range, and if AO is out of the allowable range, the control rods can immediately guide AO back to the allowable range (Patent Document 1, Non-Patent Document 1).
In addition, this inventor also invented a xenon oscillation control method described in Japanese Patent No. 3202430 (Patent Document 2, Non-Patent Document 2, Non-Patent Document 3). The xenon oscillation control method employs an axial offset of the current power distribution (AOP) in a nuclear reactor core, an axial offset of the power distribution which would give the current xenon distribution under equilibrium condition (xenon-corresponding axial offset of the current power distribution: AOX) and an axial offset of the power distribution which would give the current iodine distribution under equilibrium condition (iodine-corresponding axial offset of the current power distribution: AOI). Xenon oscillation can be suppressed by inserting or withdrawing control rods, so as to guide a trajectory to plot a parameter DAOPX (=AOP−AOX) on X axis and a parameter DAOIX (=AOI−AOX) on Y axis, to the origin of the coordinates.
Patent Literature 1: Japanese Patent Application Laid-open No. 2000-121779
Patent Literature 2: Japanese Patent Publication No. 3202430
Non Patent Literature 1: “Load-following operation of PWR”, The Thermal and Nuclear Power, Vol. 31, No. 2.
Non Patent Literature 2: “Optimum control method for axial-direction xenon oscillation of PWR based on online data processing of axial offset of the power distribution”, Journal of The Atomic Energy Society of Japan, Vol. 33, No. 3.
Non Patent Literature 3: “Improvement on axial-offset trajectory method for xenon oscillation control in load-following operation”, Journal of The Atomic Energy Society of Japan, Vol. 38, No. 1.
Since the above conventional “Power Distribution Control Method” merely controls AO within an allowable range, this method is capable of preventing significant xenon oscillation, but may not be capable of suppressing xenon oscillation after it occurred. Consequently, additional technical measures must be taken to control xenon oscillation. The control of xenon oscillation exclusively depends on power distribution information, leading to various limited operating conditions, such as changes in allowable range in accordance with power value and making it difficult to efficiently operate a nuclear reactor.
Also, because the invention described in the above Patent Document 1 controls existing xenon oscillation in order to assuredly and efficiently suppress the same, this invention is not appropriate for power distribution control.
The present invention is invented in order to solve the above-mentioned problems. The objective of the present invention is to provide at least one of suppressing xenon oscillation by controlling xenon oscillation at the same time as controlling the axial power distribution inside the reactor core by an operation with simplicity and clear purpose and reliving work load for suppressing xenon oscillation.
According to an aspect of the present invention, an axial power distribution control method includes: an axial offset calculation step of calculating an axial offset of the current power distribution, an axial offset of the power distribution which would give the current xenon distribution under equilibrium condition, and an axial offset of the power distribution which would give the current iodine distribution under equilibrium condition, using the following expressions (1) to (3) or (1)′ to (3)′, respectively, based on a relative power (PT) in the upper half of the nuclear reactor core and a relative power (PB) in the lower half of the nuclear reactor core; a parameter calculating step of calculating a xenon parameter represented by using a difference between the axial offset of the current power distribution and xenon-corresponding axial offset of the current power distribution during an operation of the reactor and an iodine parameter represented by using a difference between the iodine-corresponding axial offset of the current power distribution and the xenon-corresponding axial offset of the current power distribution during the operation of the reactor; and
a control rod moving step of controlling the movement of a control rod in such a manner that the xenon parameter and the iodine parameter move toward a major axis of an ellipse drawn by the xenon parameter and the iodine parameter which are calculated in the parameter calculating step. In order to ensure the safety of the core, these calculations are based on required parameters such as, the allowable range of both the xenon parameter and the iodine parameter and the xenon parameter and the iodine parameter which are calculated in the parameter calculating step.
Core axial offset of the current power distribution:
(PT−PB) or (PT−PB)/(PT+PB) Expression (1)
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX) or (PTX−PBX)/(PTX+PBX) Expression (2)
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI) or (PTI−PBI)/(PTI+PBI) Expression (3)
Core axial offset of the current power distribution:
(PT−PB)/(PT+PB) Expression (1)′
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX)/(PTX+PBX) Expression (2)′
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI)/(PTI+PBI) Expression (3)′, where
PTX: relative power in the upper half of the core that would give the current xenon concentration under equilibrium condition,
PBX: relative power in the lower half of the core that would give the current xenon concentration under equilibrium condition,
PTI: relative power in the upper half of the core that would give the current iodine concentration under equilibrium condition, and
PBI: relative power in the lower half of the core that would give the current iodine concentration under equilibrium condition.
The present invention controls a movement of the control rod, based on parameters (DAOPX and DAOIX) and their allowable ranges (DAOPX
Advantageously, the axial power distribution control method further includes a trajectory display step including, after the parameter calculating step and before the control-rod moving step, displaying an allowable range trajectory drawn by the allowable range of the xenon parameter and the allowable range of the iodine parameter on a display unit by setting the allowable range of the xenon parameter on one axis and the allowable range of the iodine parameter on other axis in a Cartesian coordinate system, and displaying a trajectory obtained by setting the xenon parameter calculated at the parameter calculating step on the one axis and the iodine parameter calculated at the parameter calculating step on the other axis on the display unit.
Advantageously, in the axial power distribution control method, the control-rod moving step includes performing a movement control of the control rod in such a manner that the xenon parameter and the iodine parameter move toward the major axis of the ellipse before at least one of the xenon parameter and the iodine parameter calculated at the parameter calculating step exceeds at least one of the allowable range of the xenon parameter and the allowable range of the iodine parameter.
Advantageously, in the axial power distribution control method, in a case where the allowable range of the xenon parameter is set on a horizontal axis of the Cartesian coordinate system and the allowable range of the iodine parameter is set on a vertical axis of the Cartesian coordinate system, the performing includes performing the movement control of the control rod in such a manner that the xenon parameter and the iodine parameter move toward the major axis of the ellipse upon the xenon parameter and the iodine parameter entering an area that is surrounded by the horizontal axis, the major axis of the ellipse, and the allowable range trajectory.
Advantageously, in the axial power distribution control method further includes an allowable range excess determination step of determining whether at least one of the xenon parameter and the iodine parameter calculated at the parameter calculating step exceeds at least one of the allowable range of the xenon parameter and the allowable range of the iodine parameter, before the control-rod moving step. When at least one of the xenon parameter and the iodine parameter exceeded at least one of the allowable range of the xenon parameter and the allowable range of the iodine parameter, the control-rod moving step includes performing the movement control of the control rod in such a manner that the xenon parameter and the iodine parameter move toward the major axis of the ellipse drawn by the xenon parameter and the iodine parameter.
Advantageously, the axial power distribution control method further includes a alarming step of alarming a result of determination, when it is determined that at least one of the xenon parameter and the iodine parameter exceeded at least one of the allowable range of the xenon parameter and the allowable range of the iodine parameter at the allowable range excess determination step.
According to another aspect of the present invention, an axial power distribution control supporting device includes: an axial offset calculation step of calculating an axial offset of the current power distribution, an axial offset of the power distribution which would give the current xenon distribution under equilibrium condition, and an axial offset of the power distribution which would give the current iodine distribution under equilibrium condition, using the following expressions (1) to (3) or (1)′ to (3)′, respectively, based on a relative power (PT) in the upper half of the nuclear reactor core and a relative power (PB) in the lower half of the nuclear reactor core; a parameter calculating step of calculating a xenon parameter represented by using a difference between the axial offset of the current power distribution and xenon-corresponding axial offset of the current power distribution during an operation of the reactor and an iodine parameter represented by using a difference between the iodine-corresponding axial offset of the current power distribution and the xenon-corresponding axial offset of the current power distribution during the operation of the reactor; and
a control rod moving step of controlling the movement of a control rod in such a manner that the xenon parameter and the iodine parameter move toward a major axis of an ellipse drawn by the xenon parameter and the iodine parameter which are calculated in the parameter calculating step. In order to ensure the safety of the core, these calculations are based on required parameters such as, the allowable range of both the xenon parameter and the iodine parameter and the xenon parameter and the iodine parameter which are calculated in the parameter calculating step.
Core axial offset of the current power distribution:
(PT−PB) or (PT−PB)/(PT+PB) Expression (1)
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX) or (PTX−PBX)/(PTX+PBX) Expression (2)
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI) or (PTI−PBI)/(PTI+PBI) Expression (3)
Core axial offset of the current power distribution:
(PT−PB)/(PT+PB) Expression (1)′
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX)/(PTX+PBX) Expression (2)′
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI)/(PTI+PBI) Expression (3)′, where
PTX: relative power in the upper half of the core that would give the current xenon concentration under equilibrium condition,
PBX: relative power in the lower half of the core that would give the current xenon concentration under equilibrium condition,
PTI: relative power in the upper half of the core that would give the current iodine concentration under equilibrium condition, and
PBI: relative power in the lower half of the core that would give the current iodine concentration under equilibrium condition.
The present invention displays, upon suppressing the xenon oscillation, the parameters (DAOPX and DAOIX) and their allowable ranges (DAOPX
Advantageously, the axial power distribution control supporting device further includes a control-rod moving unit that performs a movement control of a control rod in such a manner that the xenon parameter and the iodine parameter move toward a major axis of an ellipse drawn by the xenon parameter and the iodine parameter, when it is determined that at least one of the xenon parameter and the iodine parameter calculated by the parameter calculation unit exceeds at least one of the allowable range of the xenon parameter and the allowable range of the iodine parameter required for ensuring the safety of the core.
According to the present invention, it is possible to control a xenon oscillation in a simultaneous manner by simply controlling an axial power distribution in a reactor by a simple operation with a clear purpose and to suppress the xenon oscillation.
Exemplary embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the following mode for carrying out the invention (hereinafter, “embodiment”). In addition, constituent elements in the following embodiments include those that can be easily assumed by persons skilled in the art or that are substantially equivalent, which are so-called “equivalents”.
The reactor core 12 contains plural fuel rods as a nuclear fuel therein. The control rod 13 is driven by the control rod driving mechanism 14 which inserts or withdraws the control rod 13 from the reactor core 12. In this embodiment, “axial(ly)” corresponds to an axial direction of the reactor core 12, specifically a longitudinal direction of the fuel rods and a driving direction of the control rod 13. In this embodiment, axial xenon oscillation is described, because it is more commonly observed in an axial direction in the pressurized water reactor.
The control rod driving mechanism 14 is driven by the later-mentioned arithmetic processing unit 5 to drive the control rod 13 vertically. The ex-core neutron flux detectors 15a and 15b detect neutron fluxes released from upper and lower halves of the reactor core 12 to ex-core, respectively. The nuclear instrumentation system 16 calculates a relative power (PT) of the upper half of the reactor core and a relative power (PB) of the lower half of the reactor core, based on detection values on ex-core neutron flux detectors 15a and 15b. In this embodiment, a relative power is a value given by normalizing a rated power of the nuclear reactor 10 to 1.0.
The axial power distribution control device 1 of this embodiment, as shown in
The memory unit 4, included in the axial power distribution control device 1, comprising a hard disk and a random access memory (RAM), as shown in
The control-information storage unit 42 stores an allowable range with regard to the axial offset of the current power distribution in the reactor core 12 of the nuclear reactor 10 (hereinafter briefly called “AOP”). The allowable range is determined according to characteristics of the reactor core 12 in accordance with safety analysis of the reactor core 12 to reduce negative effects of xenon oscillation introduced as an axial power of the reactor core 12 changes and to ensure the safety of the reactor core 12.
The arithmetic processing unit 5 included in the an axial power distribution control device 1 comprises central processing unit (CPU). As shown in
That is, by the arithmetic processing unit 5 reading and executing the axial power distribution control program 1a, functions of the relative power acquisition unit 51, the axial offset calculation unit 52, the parameter calculation unit 53, the trajectory display unit 54, the allowable range determining unit 55, the control-rod moving unit 56, and the alarming unit 57 are realized. Meanwhile, in order for the axial power distribution control device 1 to realize a function of the axial power distribution control supporting device according to the present embodiment, it suffices with at least the axial offset calculation unit 52, the parameter calculation unit 53, and the trajectory display unit 54.
Each component of the arithmetic processing unit 5 will be described in more detail. The relative power acquisition unit 51 acquires relative powers PT and PB in upper and lower regions of the reactor core 12. In this embodiment, the relative power acquisition unit 51 acquires relative powers PT and PB from the nuclear instrumentation system 16 at a specified time interval to provide them to the axial offset calculation unit 52.
The axial offset calculation unit 52 calculates the above-mentioned AOP, an axial offset of the power distribution which would give the current xenon distribution under equilibrium condition (xenon-corresponding core axial offset of the power distribution), and an axial offset of the power distribution which would give the current iodine distribution under equilibrium condition (iodine-corresponding core axial offset of the power distribution).
The axial offset calculation unit 52 acquires relative powers PT and PB from the relative power acquisition unit 51 to calculate the core axial offset of the power distribution, the xenon-corresponding axial offset of the power distribution, and the iodine-corresponding axial offset of the power distribution from the following expressions (1) to (3) or (1)′ to (3)′, respectively. The expressions (1) to (3) are for calculating differences between the relative powers PT and PB, relative powers PTX and PBX for the xenon concentration, and relative powers PTI and PBI for the iodine concentration, respectively, and the expressions (1)′ to (3)′ are for calculating values obtained by dividing the expressions (1) to (3) by a total core relative powers
P=(PT+PB)=(PTX+PBX)=(PTI+PBI).
Core axial offset of the power distribution: (PT−PB)=ΔI or (PT−PB)/(PT+PB) Expression (1)
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX), or (PTX−PBX)/(PTX+PBX) Expression (2)
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI)), or (PTI−PBI)/(PTI+PBI) Expression (3)
Core axial offset of the power distribution: (PT−PB)/(PT+PB)=AOP Expression (1)′
Xenon-corresponding core axial offset of the power distribution: (PTX−PBX)/(PTX+PBX)=AOX Expression (2)′
Iodine-corresponding core axial offset of the power distribution: (PTI−PBI)/(PTI+PBI)=AOI Expression (3)′, where
PTX: relative power in the upper half of the core that would give the current xenon concentration under equilibrium condition,
PBX: relative power in the lower half of the core that would give the current xenon concentration under equilibrium condition,
PTI: relative power in the upper half of the core that would give the current iodine concentration under equilibrium condition, and
PBI: relative power in the lower half of the core that would give the current iodine concentration under equilibrium condition.
Here, methods for calculating AOX and AOI will be described in more detail. Changes in average xenon concentrations XT and XB in the upper half of the reactor core and the lower half of the reactor core are calculated according to the following Expressions (4) and (5), respectively, by the axial offset calculation unit 52.
dX
T
/dt’y
xΣfφ0PT+λIIT−(σaφ0PT+λX)XT Expression (4)
dX
a
/dt=y
xΣfφ0PB λIIB−(σaφ0PB+λX)XB Expression (5)
Changes in average iodine concentrations IT and IB in the upper half of the reactor core and the lower half of the reactor core are calculated according to the following Expressions (6) and (7), respectively.
dI
T
/dt=y
IΣfφ0PT−λIIT Expression (6)
dI
B
/dt=y
IΣfφ0PB−λIIB Expression (7), where
yX and yI: xenon and iodine yields from nuclear fission,
λX and λI: decay constant of xenon and iodine,
Σf: macroscopic nuclear fission cross section,
σa: microscopic absorption cross section of xenon, and
φ0: mean neutron flux with rated power.
Average xenon concentrations XT and XB, and average iodine concentrations IT and IB in the upper half of the reactor core and the lower half of the reactor core are calculated by integrating the above Expressions (4) to (7) by the axial offset calculation unit 52. Meanwhile, xenon concentrations XTEq and XBEq under equilibrium condition are calculated using relative powers PTEq and PBEq under equilibrium condition in the upper and lower halves of the reactor core using the following Expressions (8) and (9).
X
T
Eq=(yI+yX)Σfφ0PTEq/(σaφ0PTEq+λX) Expression (8)
X
B
Eq=(yI+yX)Σfφ0PBEq/(σaφ0PBEq+λX) Expression (9)
Iodine concentrations ITEq and IBEq under equilibrium condition in the upper and lower halves of the reactor core are calculated using relative powers PTEq and PREq under equilibrium condition in the upper and lower halves of the reactor core using the following Expressions (10) and (11).
I
T
Eq
=y
IΣfφ0PTEq/λI Expression (10)
I
B
Eq
=y
IΣfφ0PBEq/λI Expression (11)
While xenon concentrations XT and XB in the upper and lower halves of the reactor core are given by the above Expressions (8) and (9), their corresponding power levels PTX and PBX are calculated by the axial offset calculation unit 52. Consequently, AOX can be determined by the following Expression (12).
AO
X=(PTX−PBX)/(PTX+PBX)=(yI+yX) Σf(XT−XB)/{(yI+yX) Σf(XT−XB)−2σaXTXB} Expression (12)
Likewise, AOI can be calculated by the following Expression (13).
AO
I=(PTI−PBI)/(PTI+PBI)=(IT−IB)/(IT+IB) Expression (13)
The parameter calculation unit 53 calculates a parameter DAOPX and a parameter DAOIX. Specifically, the parameter calculation unit 53 acquires AOP, AOX and AOI from the axial offset calculation unit 52 to calculate a parameter DAOPX (=AOp−AOX) and a parameter DAOIX (=AOI−AOX). The parameter DAOPX is a xenon parameter represented by using a difference between AOP and AOX, and the parameter DAOIX is an iodine parameter represented by using a difference between AOI and AOX.
Although DAOPX and DAOIX are used as the xenon parameter and the iodine parameter, respectively, in the present embodiment, values obtained by multiplying DAOPX and DAOIX by the total relative output P of the reactor 10 can be used as the xenon parameter and the iodine parameter instead. In this case, the xenon parameter becomes DAOPX×P={(PT−PB)/(PT+PB)−(PTX−PBX)/(PTX+PBX))×P, and the iodine parameter becomes DAOIX×P=((PTI−PBI)/(PTI+PBI)−(PTX−PBX)/(PTX+PBX)}×P.
Because P=(PT+PB)=(PTX+PBX)=(PTI+PBI), the xenon parameter DAOPX×P becomes (PT−PB)−(PTX−PBX), and the iodine parameter becomes (PTI−PBI)−(PTX−PBX). That is, the xenon parameter DAOPX×P is a difference between the core axial offset of the power distribution (PT−PB) and the xenon-corresponding core axial offset of the power distribution (PTX−PBX) (Expression (1)-Expression (2)). The iodine parameter DAOIX×P is a difference between the iodine-corresponding core axial offset of the power distribution (PTI−PBI) and the xenon-corresponding core axial-direction output-distribution offset (PTX−PBX) (Expression (3)-Expression (2)). Because using DAOPX×P as the xenon parameter and DAOIX×P as the iodine parameter can give a generality with respect to the output change of the reactor 10, it is possible to monitor the reactor 10 on a steady basis even when the output of the reactor 10 is not constant.
In a case where load following operation changes power, a control method of this embodiment must be modified. Consequently, the calculation of AOX needs special consideration. (0042] First of all, because the above Expressions (4) and (5) include terms of products of powers PT and PB and xenon concentrations XT and XB, a change in xenon concentration is nonlinear to the power of each region of a reactor core 12. Therefore, as shown in an expression of xenon concentration under equilibrium condition and power (the above Expressions (8) and (9)), xenon concentration under equilibrium condition is asymptotic to (yI+yX) Σf/σa as a power increases.
If xenon concentration approaches the asymptotic value, a power obtained by inverse calculation from this value can be infinite value. For instance, such xenon concentration can be found when the power is reduced from a rated power to a partial power. Specifically, AOX obtained using the above Expression (12) can be significantly large and can significantly deviate from a value obtained under actual operating conditions. The trajectory would be divergent in this case.
The above problem can be solved by defining AOX as an axial offset of the axial power distribution which would give the current xenon offset (Xr) under equilibrium condition at the operating core power.
Xenon offset Xr is defined by the following expression.
X
r=(XT−XB)/(XT+XB) Expression (14)
S By substituting the above Expressions (8) and (9) for the above Expression (14),
X
r=λX(PT−PB)/{λX(PT+PB)+2σaφ0PTPB} Expression (15)
By definition, PT and PB are expressed by the following expressions.
P
T
=P(1+AOX) Expression (16)
P
B
=P(1−AOX) Expression (17), where
Here, P is the operating power which is obtained as measured value. By the above-mentioned definition, P is calculated from PTX and PBX obtained by inverse operation from xenon concentration, resulting in a difference from actual power.
By substituting the above Expressions (16) and (17) for the above Expression (15) to solve AOX, the AOX is determined by the following Expression (18). Using the Expression (18), a control method of this embodiment can be applied under any operational conditions.
AO
X={−1+√(1−4AC)}/2A Expression (18), where
A=σ
aφ0PXr/λX, and
i C=−Xr−A.
The trajectory display unit 54 displays a trajectory obtained by plotting the parameters (DAOPX and DAOIX) (plot trajectory) and the allowable range trajectory drawn by a trajectory of the allowable ranges (DAOPX
When ΔI shown in the expression (1) is used as the core axial offset of the power distribution, the trajectory display unit 54 displays a trajectory obtained by plotting values (DAOPX×P and DAOIX×P) obtained by multiplying each of the parameters (DAOPX and DAOIX) by the total relative output P (plot trajectory) on the display unit 2. Specifically, the trajectory display unit 54 acquires the parameters (DAOPX×P and DAOIX×P) calculated by the parameter calculation unit 53, and displays a plot trajectory obtained by setting the parameter (DAOPX×P) on the X-axis (horizontal axis that is one axis) and the parameter (DAOIX×P) on the Y-axis (vertical axis that is the other axis) in the Cartesian coordinate system on the display unit 2. Similarly, the trajectory display unit 54 displays the allowable range (DAOPX
In the Cartesian coordinate system, the parameter (DAOPX) and the allowable range (DAOPX
It is known that a plot trajectory of parameters (DAOPX, DAOIX) involves the characteristics in the following (1) to (5).
The allowable ranges (DAOPX
The allowable range DAOPX
The allowable range determining unit 55 determines whether the parameters (DAOPX and DAOIX) exceed the allowable ranges (DAOPX
The control-rod moving unit 56 performs a movement control, such as inserting, drawing, and stopping, of the core of the control rod 13 by controlling the control rod driving mechanism 14. In the present embodiment, an operator monitors the allowable range trajectory displayed on the display unit 2 and the parameters (DAOPX and DAOIX) at the current time calculated by the parameter calculation unit 53. During the monitoring, for example, when the parameters (DAOPX and DAOIX) are about to exceed the allowable range trajectory (that is, before the parameters (DAOPX and DAOIX) exceed the allowable ranges (DAOPX
The alarming unit 57 makes a warning that AOP has exceeded the allowable range. In the present embodiment, the alarming unit 57 changes a display color of the plot point drawn by the trajectory display unit 54 upon acquiring an output signal indicating that AOP has exceeded the allowable range from the allowable range determining unit 55. For example, when the plot point at the normal time (when the parameters (DAOPX
In this embodiment, the control rod 13 may be moved so that a plot point of the ellipse trajectory indicated on the display unit 2 is guided to the major axis of the ellipse. In fact, this method for operating a control rod is invented by this inventor based on unconventional findings. This inventor found that AOP is constant in case of a plot point lying on the major axis of the ellipse trajectory.
The above findings will be described in more detail with reference to the drawings.
As shown in
The parameter DAOPX is defined as (AOP−AOX), and the major axis a and minor axis of an ellipse formed by the trajectory of said parameters is proportional to AOP (expressed as amplitude in
In a case where the control rod 13 is moved, a plot point is preferably moved to the major axis, but may be as close as possible. As a result, since the rate of change in AOP becomes a minimum level, it is possible to suppress xenon oscillation. As long as no other disturbance is observed, xenon oscillation develops with smaller amplitude after the plot point is moved, thereby making the plot point gradually approach the origin and inevitably suppressing xenon oscillation.
In this embodiment, the control rod 13 is manually operated by an operator, but this invention is not limited thereto. The control rod moving unit 56 may automatically control the control rod 13. In this case, the control rod moving unit 56 acquires an alarm signal from the allowable range determining unit 55 to calculate a distance on X axis from the current plot point to the major axis of the ellipse trajectory. Based on the distance, a movement volume of the control rod 13 is calculated and an operation signal of inserting the control rod 13 by the steps is given to the control rod driving mechanism 14. Also in this case, the control-rod moving unit 56 performs a movement control of the control rod in such a manner that the plot point is induced toward the major axis of the ellipse. Since the relationship between motion steps of the control rod 13 and motion steps of a plot point varies with time, arithmetic processing is executed in accordance with conditions corresponding thereto.
The axial power distribution control method according to the present embodiment is explained next with reference to
Thereafter, the process proceeds to Step S2, and the axial offset calculation unit 52 calculates the axial offsets of the power distribution AOP, AOX, and AOI based on PT and PT acquired by the relative power acquisition unit 51 by using the relational expressions (1) to (3) (axial offset of the power distribution calculating step). At Step S3, the parameter calculation unit 53 calculates the parameter DAOPX and the parameter DAOIX from the axial offsets of the power distribution AOP, AOX, and AOI calculated by the axial offset calculation unit 52 (parameter calculating step).
Thereafter, the process proceeds to Step S4, and the trajectory display unit 54 acquires a allowable range trajectory from the control-information storage unit 42 and displays it on the display unit 2 (a dotted line L shown in
Thereafter, the process proceeds to Step S5, and it is determined whether to move the control rod 13. In the present embodiment, an operator compares the latest plot point of the parameter DAOPX and the parameter DAOIX displayed on the display unit 2 with the allowable range trajectory L of the allowable ranges (DAOPX
When a result of the determination is “NO” at Step S5, controls from Step S1 to Step S5 are repeated. In this case, because the trajectory display unit 54 displays the plot point indicating the parameters (DAOPX and DAOIX) on the display unit 2 at Step S4, a trajectory of the plot point is displayed on the display unit 2 at predetermined time intervals. Once the allowable range trajectory L is displayed on the display unit 2, the display of the allowable range trajectory is continued as it is from then on.
On the other hand, when the result of the determination is “YES” at Step S5, that is, when the latest plot point is about to exceed the allowable range trajectory L (PT1 in
With this configuration, because the change rate of the core axial offset of the power distribution AOP is minimized as long as there is no other disturbance, it is possible to suppress the xenon oscillation. In addition, because the xenon oscillation makes a progress in a direction with which the amplitude is decreased after moving the plot point, even if it is left unattended after that, the plot point approaches the origin O, and the xenon oscillation progresses toward a direction of being naturally extinguished. After performing the movement control of the control rod 13, the process returns to START, and monitoring the operation state of the reactor 10 is continued.
The major axis a of the elliptical trajectory is the major axis a of the ellipse formed by a trajectory of the plot point of the parameters (DAOPX and DAOIX) calculated by the parameter calculation unit 53. Because the major axis of the ellipse exists at the first quadrant and the third quadrant, which is inclined at a predetermined angle (around 36 degrees) to the horizontal axis regardless of a magnitude of the xenon oscillation as described above, the allowable range trajectory L becomes an ellipse of which the major axis exists at the first quadrant and the third quadrant, in the same manner as the elliptical trajectory of the plot point of the parameters (DAOPX and DAOIX). Therefore, at Step S6, the control rod 13 can be operated in such a manner that the latest plot point of the parameters (DAOPX and DAOIX) moves toward the major axis of the allowable range trajectory L.
When the latest plotting point is about to exceed the allowable range trajectory L (PT1 in
When the control rod 13 is controlled by the control-rod moving unit 56 in an automatic manner, at Step S5, the allowable range determining unit 55 determines whether at least one of the latest parameter DAOPX and the latest parameter DAOIX exceeded at least one of the allowable range DAOPX
Alternatively, an operator can operate the control rod 13 based on the warning from the alarming unit 57. In this case, the allowable range determining unit 55 determines whether at least one of the latest parameter DAOPX and the latest parameter DAOIX exceeded at least one of the allowable range DAOPX
(0072) The above-mentioned embodiment includes the following advantages,
As described above, the axial power distribution control method and the axial power distribution control supporting device according to the present invention are effective in controlling output distribution in an axial direction of a reactor.
1 Axial power distribution control device
1
a Axial power distribution control program
2 display unit
3 input unit
4 storage unit
5 arithmetic processing unit
10 reactor
11 pressure vessel
12 core
13 control rod
14 control rod driving mechanism
15
a ex-core neutron-flux detector
15
b in-core neutron-flux detector
16 nuclear instrumentation system
41 program storage unit
42 control-information storage unit
51 relative power acquisition unit
52 axial offset calculation unit
53 parameter calculation unit
54 trajectory display unit
55 allowable range determining unit
56 control-rod moving unit
57 alarming unit
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-038136 | Feb 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/052474 | 2/18/2010 | WO | 00 | 10/26/2011 |
